*******137B - kinetics Flashcards
describe this graph
As time goes on the conc of A decreases and is replaced by B
what does the value of the rate of a reaction actually mean
how fast the conversion of reactants into products is In terms of concentration/ how quickly are the reactants consumed
what is the change in A per unit time on the right graph compared to the left
on the left the change in A per unit time (e.g per second) is constant, but on the right it is not constant
-rate starts off high then decreases
how would you work out the change in A per unit time at each of these points on a non linear graph
tangent at the point/ gives an estimate of what the change in A would be per time if the line was straight
what do each of these equations mean
the rate at which A changes/disappears, is also the rate at which B is formed
-inverse signs because the graph curves are going the opposite ways so A rate of loss must be negative and B gains must be positive
this graph and equation makes sense
-B’s curve is deeper because it is being consumed twice as fast
-what would the rate equation be for A, B and C if the rate is amount consumed/made over time
A, B, C is in 1:2:1 ratio
- A and C have normal conc/time with their respected signs
-B is consumed twice as fast so has a half
note is B was any interger it would be 1/X
lecture 1
most of the stuff you need for the course
what is v and k and the letters
v= rate
k= rate constant
[A] = conc of A to the power of something (0 if zero order, 1 if first order)
what are the rate orders of [H2], [Br2] and [HBr]
undefined order overall because we cannot add up all the rate orders if we dont know them
these are examples of elementary processes. molecules of A coming together to make B. Describe maybe the conditions for each example and where you would see it
- no collision- sometimes a molecule will just flip into a different form/ absorbs light and decomposes
- 2 molecules A making one molecule of B
- is very rare but can happen in gas form under very high pressure
what would be the rate equation for this: v, k and [A]
for this reaction, the probability of A becoming P is constant per molecule per unit time
-therefore
v ∝ P
for this reaction, the probability of A becoming P is constant per molecule per unit time
-therefore
v ∝ [A]
what is the overall reaction order of this bimolecular reaction
second order
how can this rate equation be changed into a proportionality equation due to the fact that if we increase the amount of A its going to be proportional to the amount the rate increases by
rate is proportional to the conc of A and B by the same amount
what is the rate law for this reaction including v, k and concentrations
overall second order with respect to A
the units of the rate constant (k) change depending on the order.
This is is first order equation- what are the units of k
what are the units of k for this second order reaction
what are the units of k for a third order reaction
each has a different rate constant
-writing down equations for rate of change of A and C versus time
k is minus for A because A Is being used uo
k is + for C because C is being produced
B is more complicated
-b produced in first step but consumed in second
-rates are same as constant amount of ‘stuff’ in the reaction/ fixed amount so B is produced at same rate A Is produced….on slide
rate of change of B of function of time (equation on slide)
what is intergrated equation for C equation?
d[C] = k2[B] dt
dont have to know maths specifically
c on graph lags behind formation of B
what does it mean if k1» k2
-therefore which k would the overall rate of the reaction be dependant on
A is being converted into B, much faster than B is converted to C
-overall rate is limited by the slowest step [K1]
what does it mean if k1«_space;k2
-therefore which k would the overall rate of the reaction be dependant on
A is slowly converted to B, but B is almost immediately changed into C
-overall rate is dependant on slowest step [K2]
equilibrium slide
A and B have 2 elementary processes
-becuase A is turned to B, but B is also turned to A
-meaning 2 terms in the rate equation
[new terms for rate of change of A and B in respect to time]
-at equilibrium rate of change of A and B are 0, [conc has stopped changing]
rearranged is kA=K-1B
KA= rate of froward process
K-1B= rate of backwards
-equation says rates are the same
last E= ratio of rate constants = Keq
pre-equilibira
rate of change of A and rate of change of B are the same,
-2 elementary proc involving A and b meaning 2 terms in rate equation -k[A][B] + k-1[C]
because formation of C is same rate as making A and B again
rate of change of C over time
-C is involved in 3 processes, formed AB reached, consumed reacting back to AB and also converted into D. 3 arrows start or end at C
-3 terms in rate eq for conc of C changing with time
-rate at which C is produced +k[A][B]
-2 processes CONSUMING C so negative bc it is being consumed
-overall rate C is being consumed at is sum of both of those rates (K-1[C] and K2[C])
K1»_space; is big, A and b quickly reach equilibrium between A,B and C
-C has gone to max amount
-and is slowly converted into D
therefore take top equation and equal it to 0
the final equaition is an equilibrium constant for pre equilibrium step C/AB =…..
2nd order overall, 1st order in respect to A and B
types of reactions
1. consecutive reactions-slow step is rate limiting step
2. equilibrium - forward and reverse reaction have equal rates. Using this, we can write rate constant as a ratio of k
3. pre-equillbira. Something equilibrates then forms a final product
-if eq is fast compared to the other step, we can get a rate constant and a pseudo second order process
what are the intergrated rate laws, and the linear rate laws
how would you get from one to the other
how would you get from one to the other
how would you get from one to the other
how do you get from the integrated rate law to the linear one
how do you get from the integrated rate law to the linear one
how do you get from the integrated rate law to the linear one
what graphs would these plot
How to work out the half life of [A]
using the half life method
what are the 2 elementary processes that make up this reaction
what is the change in conc of A with respect to time
what is the change in conc of A with respect to time
what is the change in conc of C with respect to time
what is the equation for the change in conc of B with respect to time
-do the equations for A and C first
-need to do the rest of lecture 4 [isolation method]
-finish lecture 5 some of the consecutive reactions
what is the rate of change of conc for A and B with respect to time
what is the rate of change of conc for A and B with respect to time
how do you get Keq from this equation
-Keq is the ratio between the two equilibrium constants [K]
fill in the rate equations
what is the equation for the pre-equillbira formed
how would you re-write the equation in logarithmic form
